An Update on Drugs Used for Lumbosacral Epidural Anesthesia and Analgesia in Dogs

Whether epidural analgesia is a better method than parenteral opioids for postoperative pain control remains controversial. To systematically review the efficacy of postoperative epidural analgesia vs parenteral opioids, the primary alternative technique. Studies were identified primarily by searching the National Library of Medicine's PubMed database (1966 to April 25, 2002) and other sources for studies related to postoperative epidural analgesia. Inclusion criteria were a comparison of epidural therapy vs parenteral opioids for postoperative analgesia, measurement of pain using a visual analog scale (VAS) or numeric rating scale, randomization of patients to either therapy, and adult patients (> or =18 years). A total of 1404 abstracts were identified, 100 of which met all inclusion criteria. Each article was reviewed and data extracted from tables, text, or extrapolated from figures as needed. Weighted mean pain scores, weighted mean differences in pain score, and weighted incidences of complications were determined by using a fixed-effect model. Epidural analgesia provided better postoperative analgesia compared with parenteral opioids (mean [SE], 19.40 mm [0.17] vs 29.40 mm [0.20] on the VAS; P<.001). When analyzed by postoperative day, epidural analgesia was better than parenteral opioids on each postoperative day (P<.001 for each day after surgery). For all types of surgery and pain assessments, all forms of epidural analgesia provided significantly better postoperative analgesia compared with parenteral opioid analgesia (P<.001 for all), with the exception of thoracic epidural analgesia vs opioids for rest pain after thoracic surgery (weighted mean difference, 0.6 mm; 95% confidence interval, -0.3 to 1.5 mm; P =.12). The complication rates were lower than expected for nausea or vomiting and pruritus but comparable with existing data for lower extremity motor block. Epidural analgesia, regardless of analgesic agent, location of catheter placement, and type and time of pain assessment, provided better postoperative analgesia compared with parenteral opioids.

Ketamine hydrochloride is a well known general anesthetic and short acting analgesic in use for almost 3 decades. The role of the NMDA receptor in the processing of nociceptive input has led naturally to renewed clinical interest in N-methyl-D-aspartate (NMDA) receptor antagonists such as ketamine. This paper reviews the use and efficacy of low-dose ketamine in the management of acute postoperative pain. The literature was obtained from a computer search of the MEDLINE database from 1966 through December 1998. Studies were included for review if they were randomized, prospective, controlled, double-blind and reported pain scores. We evaluate the clinical literature and discuss the efficacy of low-dose ketamine in the management of acute postoperative pain when administered alone or in conjunction with other agents via the oral, intramuscular, subcutaneous, intravenous and intraspinal routes. Low-dose ketamine is defined as a bolus dose of less than 2 mg/g when given intramuscularly or less than 1 mg/kg when administered via the intravenous or epidural route. For continuous i.v. administration low-dose ketamine is defined as a rate of < or =20 microg/kg per min. We conclude that ketamine may provide clinicians with a tool to improve postoperative pain management and to reduce opioid related adverse effects. The evidence suggests that low-dose ketamine may play an important role in postoperative pain management when used as an adjunct to local anesthetics, opioids, or other analgesic agents. Further research is required in the following areas: (a) dose-finding studies for ketamine as an adjunct to opioids and local anesthetics (b) efficacy and optimal route of administration (c) the role of S(+)-ketamine; (d) the influence of ketamine on long-term outcome such as chronic pain (e) long-term physical and chemical stability of mixtures containing ketamine (f) spinal toxicity of ketamine and (g) effects of low-dose ketamine on cognitive and memory functioning after surgery.